This invention relates to teat cup assemblies for vacuum-operated milking machines including a rigid shell and a flexible inflation.
Automatic milking machines employ teat cup assemblies having a hollow, rigid outer shell and a resilient inflation including a tubular liner portion installed in the shell in a manner to form a seal at both ends of the shell and define a chamber between a shell and the liner portion. The cow's teat is inserted into the upper end of the liner portion and a milking tube portion on the lower end is connected to a so-called claw of the milking machine. During the milking operation, a vacuum maintained in the milking machine causes milk to flow from the teat and through the inflation.
One type of conventional liner has a head including a laterally extending wall having a central opening which receives a cow's teat and a downwardly extending skirt or cuff which fits snugly over the upper end of the shell. After the teat cup assembly has been removed from a cow's teat, it is suspended from a claw nipple in a manner to shut off flow. During repeated milking operations, the head of the liner can be subjected to a number of potentially damaging impacts, e.g., dropping on a concrete floor or drain grating of a milking stall, banging into a milking stall wall, another teat cup assembly or other equipment, or being stepped on by a cow.
Liners most often are made from a natural or synthetic rubber composition which is resistant to tearing or cutting from such impacts. Silicone rubbers are substantially less vunerable to attack by butterfats, teat treatment preparations and other chemicals than conventional rubber compositions used for liners. Also, silicone rubbers also have other characteristics which normally would prolong the useful life of milking machine liners. However, the tear and puncture resistance of silicone rubbers is substantially lower than for more conventional rubber compositions and liners made from a silicone rubber tend to tear and/or puncture when subjected to common occuring impacts like those mentioned above.
U.S. Pat. No. 4,651,676 discloses a teat cup assembly including a shell which is designed to protect the liner cuff against impacts. The shell includes an integral, annular flange defining an annular recess which receives and covers the cuff. Such an arrangement requires a relatively complicated mold for fabrication of the shell. The assembly relies on a wedge fit between the liner cuff and the annular flange to prevent twisting or other movement of the liner relative to the shell and also to prevent entry of water and other foreign materials into the shell, particularly during washing. The tightness of this fit can vary considerably, depending on the buildup of manufacturing tolerances.
U.S. Pat. No. 4,651,676 also discloses that the liner can be secured to the shell by applying an adhesive in the annular recess, in which case a liner could not be conveniently replaced and the entire assembly must be discarded when the liner wears out.